1. Field of the Invention
The present invention is directed to a device for ensuring sheet conveyance within a sheet processing machine.
2. Prior Art
Sheet processing machines are composed of several stations and definite operations are achieved or accomplished on the sheet at each of the stations. A problem, which always occurs in such devices, is the ensuring of a proper conveyance between two successive stations. In certain cases, the sheet is conveyed from one station to another by means of belt conveyors bridging over the gap between the two stations. However, when a sheet is transferred from one station in which the sheets are being fed one after the other to a second station where the sheets should be placed one upon the other in such a way to be shingled like tiles of a roof, it is necessary to use a conveying device consisting of upper and lower conveyors at the first station. In such a case, the upper conveyor should be slightly longer than lower coveyors so as to be able to ensure the ejection of the sheet, which may be a box blank, from between the upper and lower conveyor. As a rule, the first station in which the sheets are being conveyed one after the other, utilizes an upper and lower continuous belt conveyor arranged side by side whereas the station in which the sheets are to be shingled consist of a lower continuous belt conveyor on which several pressure rollers act to ensure the foward motion of the stream of shingled sheets supported thereon. The lower belt at the second station is driven at a slower speed than the upper and lower conveyors of the preceeding station so that the shingling of the blanks or sheets will occur.
To ensure a reliable transfer of a sheet or blank from one station to the second station and to ensure that the sheet is pushed under the driving appliance of the second station by the conveyors of the preceeding first station, the above described conveyor devices require that the blanks or sheets have an adequate stiffness. When the sheets being handled by the device easily bend and do not have the required stiffness, the bending of the sheets will impair the formation of the stream of shingled blanks or sheets and may, at the worst, create jam-ups at the transfer between the two stations which jam ups cause a stopping of the sheet processing machines. It is also noted that the majority of the sheets being processed in such a transfer station do not have the required stiffness.